Stable and reliable FinFET SRAM with improved beta ratio

ABSTRACT

Fabrication method for a semiconductor memory device and structure are provided, which includes: providing at least two mask layers over a pair of fin structures extended above a substrate, wherein a first mask layer of the at least two mask layers is orthogonal to a second mask layer of the at least two mask layers; and patterning the pair of fin structures to define a pass-gate transistor, wherein the first mask layer facilitates removing of a portion of a first fin structure of the pair of fin structures to define a first pass-gate fin portion of the pass-gate transistor, and the second mask layer protects a second fin structure of the pair of fin structures to define a second pass-gate fin portion of the pass-gate transistor.

FIELD OF THE INVENTION

The present invention relates to a semiconductor memory device and to amethod of fabricating a semiconductor memory device, and moreparticularly, to a static random access memory (SRAM) device with animproved beta ratio.

BACKGROUND

Conventional static random-access memory (SRAM) devices are generallyused in applications requiring high speed, such as, memory in a dataprocessing system, and typically consist of six transistors (6T): two Pchannel field effect transistors (PFETs) for a pull-up operation, two Nchannel field effect transistors (NFETs) for pull down, and two NFETsfor input/output (i.e. passgate) access. As the size of technology nodescontinues to decrease, fin field-effect transistors (FinFETs) areintroduced to replace planar transistors, during the fabrication of SRAMdevices. As one skilled in the art will understand, the stability of a6T SRAM cell, in general, is defined by a beta ratio which, forinstance, is the ratio of the drive currents of the pull-downtransistors to the drive currents of the respective pass-gatetransistors.

FIG. 1 illustrates a top plan view of a typical 6T SRAM device 100. Inthe embodiment illustrated, the SRAM device 100 typically includes oneor more regions, for instance, region A and region B. As one skilled inthe art will understand, during conventional SRAM fabrication a largenumber of regions A and B are provided together on a substrate. Asdepicted, each of these regions A and B include, for instance, twopass-gate transistors 112 that are electrically coupled to two pull-downtransistors 110 which, in turn, are electrically coupled to two pull-uptransistors 108, respectively. Note that, as illustrated, each of thetwo pass-gate transistors 112 include two fin structures (referred tohereinafter as “fins”) that allow electrically coupling of one pass-gatetransistor 112 to an adjacent pass-gate transistor 112. Additionally,the two fins of the pass-gate transistors 112 also enable electricalcoupling of the pass-gate transistor to the neighboring pull-downtransistors 110, respectively. Although not depicted in the figures, oneskilled in the art will understand that, a source region and a drainregion are formed at opposite ends of each of the pass-gate FinFETs 112,pull-down FinFETs 110 and pull-up FinFETs 108.

Continuing with FIG. 1, an equal number of pull-down devices andpass-gate devices provide a tradeoff between the cell size and the cellspeed. In this situation, the beta ratio is equal to 1. The unitary betaratio, for instance, could lead to undesirable issues such as, accessdisturb. As one skilled in the art will understand, higher beta ratiosare desirable to improve the stability of the SRAM cell, withoutincreasing the overall size of the SRAM cell. As understood, regions,for instance, regions A and B, are expanded to form bigger cells which,for instance, are more stable because bigger FET features are relativelymore precise.

Enhancements in semiconductor memory device structures and fabricationmethods therefor continue to be desired for enhanced performance andcommercial advantage.

BRIEF SUMMARY

Certain shortcomings of the prior art are overcome and additionaladvantages are provided through the provision, in one aspect, of amethod for forming a semiconductor memory device which includes, forinstance, providing at least two mask layers over a pair of finstructures extended above a substrate, wherein a first mask layer of theat least two mask layers is orthogonal to a second mask layer of the atleast two mask layers; and patterning the pair of fin structures todefine a pass-gate transistor, wherein the first mask layer facilitatesremoving of a portion of a first fin structure of the pair of finstructures to define a first pass-gate fin portion of the pass-gatetransistor, and the second mask layer protects a second fin structure ofthe pair of fin structures to define a second pass-gate fin portion ofthe pass-gate transistor.

In a further aspect, a semiconductor memory device which includes, forinstance, a static random-access memory (SRAM) cell including at leastone pass-gate transistor and at least one pull-down transistor, whereineach of the at least one pass-gate transistor and the at least onepull-down transistor have a pair of fin structures extended above asubstrate, and electrically coupled to each other, wherein a finstructure of the pair of fin structures is encapsulated within a gatestructure of the at least one pass-gate transistor.

In yet another aspect, a method for forming a semiconductor memorydevice which includes, for instance, providing at least two mask layersover a pair of fin structures extended above a substrate, a first masklayer of the at least two mask layers being orthogonal to a second masklayer of the at least two mask layers, where the first mask layer of theat least two mask layers facilitates modulating stability of thesemiconductor memory device, without affecting the second mask layer ofthe at least two mask layers.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

One or more aspects of the present invention are particularly pointedout and distinctly claimed as examples in the claims at the conclusionof the specification. The foregoing and other objects, features, andadvantages of the invention are apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 depicts a plan view of one embodiment of a conventional SRAMdevice;

FIG. 2 depicts a plan view of one embodiment of a structure obtainedduring static random-access memory (SRAM) fabrication process, andillustrates one or more fins disposed over the substrate, in accordancewith one or more aspects of the present invention;

FIG. 3 is a plan view of the structure of FIG. 2 with one or more firstlithographic mask layer(s) having been disposed over the fin(s), inaccordance with one or more aspects of the present invention;

FIG. 4 is a plan view of the structure of FIG. 3 with one or more cutmask layer(s) having been disposed orthogonal to the first lithographicmask layer(s) over the fin(s), in accordance with one or more aspects ofthe present invention;

FIG. 5 is a plan view of the structure of FIG. 4 after providing one ormore second lithographic mask layer(s) orthogonal to the cut masklayer(s) over the fin(s), in accordance with one or more aspects of thepresent invention;

FIG. 6 is a plan view of the structure of FIG. 5 after patterning thefin(s), for instance, using the cut mask layer(s), to define a pass-gatetransistor, in accordance with one or more aspects of the presentinvention;

FIG. 7 is a plan view of the structure of FIG. 6 with gate structure(s)having been provided over the patterned fin(s), in accordance with oneor more aspects of the present invention;

FIG. 8 is a plan view of a resultant structure of FIG. 7 after expandingthe structure during the SRAM fabrication process, in accordance withone or more aspects of the present invention; and

FIG. 9 is a plan view of an alternate embodiment of a resultantstructure of FIG. 5 with the stability of the semiconductor memorydevice having been modulated, in accordance with one or more aspects ofthe present invention.

DETAILED DESCRIPTION

Aspects of the present invention and certain features, advantages, anddetails thereof, are explained more fully below with reference to thenon-limiting examples illustrated in the accompanying drawings.Descriptions of well-known materials, fabrication tools, processingtechniques, etc., are omitted so as not to unnecessarily obscure theinvention in details. It should be understood, however, that thedetailed description and the specific examples, while indicatingembodiments of the invention, are given by way of illustration only, andnot by way of limitation. Various substitutions, modifications,additions and/or arrangements within the spirit and/or scope of theunderlying inventive concepts will be apparent to those skilled in theart from this disclosure.

The present invention provides, inter alia, a fabrication method and astructure for a SRAM device with improved beta ratio. As describedabove, and in one aspect, during conventional FinFET fabricationprocessing, and in particular, during SRAM fabrication processing, oneor more fin structures or fins residing over a substrate may be spacedapart, and during bulk FinFET or SRAM fabrication processing, more finsmay have been created than required for a particular circuit or device.Thus, a fin cut or fin removal process is employed to remove one or moreunwanted fin structures, in particular, at the pass-gate transistor ofthe SRAM device. Such removal of an unwanted fin and subsequent tuckingof the unwanted fin within an overlying gate structure at the pass-gatetransistor, for instance, could improve the beta ratio of a SRAM device.Disadvantageously, the conventional processing techniques employed couldlead to inadvertently removing the adjacent fin along with the unwantedfin, thereby resulting in performance degradation of the resultant SRAMdevice. Additionally, the conventional processing techniques employedduring the fin cut processing could, for instance, involve utilizing apair of mask layers (e.g., lithographic mask layer and cut mask layer)to pattern the various cells of the SRAM device. For instance, the cutmask layer is conventionally employed to cut the pull-up fin. As oneskilled in the art will understand, in the 14 nm and beyond technologynodes, the cut mask layer has been utilized to cut both the pull-up finand the pass-gate fin, while in the technology nodes below 14 nm, thecut mask layer has been utilized to cut the pull-up fin, resulting inconstraining the beta ratio of the SRAM device to be 1. Still further,the conventional processing techniques employed during the fin cutprocessing could, disadvantageously, result in rounding of a remainingfin portion. This rounding profile of the remaining fin portion maycause subsequent epitaxial growth problems at the source region and thedrain region of the pass-gate transistor, and for at least thisreasoning is undesirable.

In one aspect of the present invention, there is disclosed a method forforming a semiconductor memory device which includes, for instance,providing at least two mask layers over a pair of fin structuresextended above a substrate, wherein a first mask layer of the at leasttwo mask layers is orthogonal to a second mask layer of the at least twomask layers; and patterning the pair of fin structures to define apass-gate transistor, wherein the first mask layer facilitates removingof a portion of a first fin structure of the pair of fin structures todefine a first pass-gate fin portion of the pass-gate transistor, andthe second mask layer protects a second fin structure of the pair of finstructures to define a second pass-gate fin portion of the pass-gatetransistor.

In one embodiment, the patterning of the pair of fin structures with thefirst mask layer and the second mask layer provides the first pass-gatefin portion of the pass-gate transistor with squared edges. In such anembodiment, the fabrication method may include a gate structureextending at least partially over the pair of fin structures of thepass-gate transistor, and the first pass-gate fin portion of thepass-gate transistor is encapsulated within the gate structure,selective to the second pass-gate fin portion. Such encapsulation of thefirst pass-gate fin portion within the gate structure of the pass-gatetransistor enhances a beta ratio of the semiconductor memory device.

In one implementation, the first mask layer may include a firstlithographic mask layer and a cut mask layer, with the firstlithographic mask layer being orthogonal to the cut mask layer. In suchan implementation, the cut mask layer facilitates removing of theportion of the first fin structure. Further, the patterning of the pairof fin structures may include modifying the selective removal of theportion of the first fin structure with the cut mask layer to providethe first pass-gate fin portion with squared edges so as to facilitateencapsulation of the first pass-gate fin portion within the gatestructure. In another implementation, the second mask layer may includea second lithographic mask layer, with the second mask layer beingspaced parallel to the first lithographic mask layer. In such animplementation, the second mask layer and the first lithographic masklayer define the second fin portion of the pass-gate transistor.

In another embodiment, the fabrication method may include an additionalfirst lithographic mask layer, with the additional first lithographicmask layer being spaced parallel to the first lithographic mask layer.In such an embodiment, the additional first lithographic mask layerdefines a pull-up transistor, and the pull-up transistor is electricallycoupled with the pull-down transistor. In yet another embodiment, thefabrication method may include an additional pass-gate transistor, withthe additional pass-gate transistor including a first pass-gate finportion and a second pass-gate fin portion, and the additional pass-gatetransistor is in-line with the pass-gate transistor, where the firstpass-gate fin portion of the second pass-gate transistor is electricallyisolated from the first pass-gate fin portion of the pass-gatetransistor, and the second pass-gate fin portion of the second pass-gatetransistor is electrically coupled with the second pass-gate fin portionof the pass-gate transistor. In such an example, the electricalisolation of the first pass-gate fin portion of the pass-gate transistorand the first pass-gate fin portion of the additional pass-gatetransistor enhances a beta ratio of the semiconductor memory device. Forexample, the enhanced beta ratio of the semiconductor memory device maybe about 2.0 or more.

In another aspect of the present invention, there is provided asemiconductor memory device which includes, for instance, a staticrandom-access memory (SRAM) cell including at least one pass-gatetransistor and at least one pull-down transistor, where each of the atleast one pass-gate transistor and the at least one pull-down transistorhave a pair of fin structures extended above a substrate, andelectrically coupled to each other, where a fin structure of the pair offin structures is encapsulated within a gate structure of the at leastone pass-gate transistor.

In yet another aspect of the present invention, there is provided amethod for forming a semiconductor memory device which includes, forinstance, providing at least two mask layers over a pair of finstructures extended above a substrate, a first mask layer of the atleast two mask layers being orthogonal to a second mask layer of the atleast two mask layers, where the first mask layer of the at least twomask layers facilitates modulating stability of the semiconductor memorydevice, without affecting the second mask layer of the at least two masklayers.

Reference is made below to the drawings, which are not drawn to scalefor ease of understanding, wherein the same reference numbers usedthroughout different figures designate the same or similar components.

By way of example, FIGS. 2-8 depict one embodiment of a method forforming a semiconductor memory device, for example, a SRAM device withan improved beta ratio, in accordance with one or more aspects of thepresent invention. Advantageously, as described below, the two or moremask layers employed in the patterning of the fins facilitatesselectively removing a portion of the unwanted fin, leaving a patternedfin with squared edges which, for instance, are encapsulated within anoverlying gate structure, thereby creating an electrical isolationtherein, and improving the beta ratio of the resultant SRAM device.

FIG. 2 depicts a plan view of one embodiment of a structure 200 obtainedduring static random-access memory (SRAM) fabrication process, inaccordance with one or more aspects of the present invention. In theexample shown, structure 200 includes a substrate 202, which may be (inone example) a bulk semiconductor material such as, for example, a bulksilicon wafer. As another example, substrate 202 may be anysilicon-containing substrate including, but not limited to, silicon(Si), single crystal silicon (Si), polycrystalline Si, amorphous Si orthe like. Substrate structure 202 may in addition, or instead, includevarious isolations, dopings and/or device features. Optionally,substrate structure 202 may include an insulating substrate layer which,for instance, may be, or include, a buried dielectric layer such as, forexample, a buried oxide (BOX) layer, silicon-on-nothing (SON),silicon-on-insulator or the like. As one skilled in the art willunderstand, a buried oxide layer may be fabricated by employing SIMOX(Separation by Implanted Oxygen) technique which, for instance, mayinclude implanting high doses of oxygen (O⁺) ions into the siliconsubstrate, and annealing at a high temperature to form a layer of buriedoxide over the silicon substrate. In such an example, the fabrication ofthe buried oxide layer may result in a residual layer of semiconductormaterial (not shown) which, for instance, may include a siliconmaterial, being disposed over the insulating substrate layer (notshown).

Continuing with FIG. 2, one or more fin structures or fins 204 may beformed extending from substrate 202. By way of an example, fins 204 maybe formed by patterning one or more portions of substrate 202, therebycreating one or more fins 204 of the same semiconductor material as thesubstrate 202, for example, silicon material. In one example, formationof fins 204 may be achieved by patterning the substrate 202 using any ofvarious approaches including: direct lithography; sidewall imagetransfer technique; extreme ultraviolet technique (EUV); e-beamtechnique; litho-etch litho-etch or litho-freeze-litho-etch. Followingpatterning, the removal may be performed, for example, by any suitableetching process, such as, anisotropic dry etching processes, forinstance, reactive-ion-etching (RIE) process. Although not critical tothe invention, fins 204 may have any suitable height.

Continuing further with FIG. 2, although evenly spaced fins with similardimensions may be obtained after a conventional fabrication processing,in one implementation, the distance between two adjacent fins may alsobe varied depending upon the various process parameters employed. Asillustrated, while two adjacent fins (for instance, fins 204 a and 204b) may be spaced closer (for instance, distance D2), the distancebetween adjacent fins (for instance, fins 204 b and 204 c) may also bevaried by distance D1. As described further below, these variations indistances between the fins facilitates forming various pull-uptransistors, pull-down transistors and pass-gate transistors of the SRAMdevice, during subsequent fabrication processing. For instance, in oneembodiment, the pair of fins 204 a and 204 b may be utilized to form oneor more pull-down transistors and one or more pass-gate transistors,while the isolated fin 204 c may be utilized to form one or more pull-uptransistors.

FIG. 3 is a plan view of the structure of FIG. 2 with one or more firstlithographic mask layer(s) 206 having been disposed over the fin(s) 204,in accordance with one or more aspects of the present invention. By wayof an example, the first lithographic mask layer(s) 206, which, forinstance, may include, or be fabricated of a photoresist material or aphotosensitive dielectric material, such as, photosensitive polyimide,and may be deposited using conventional deposition processes, such as,spin-on coating. This first lithographic mask layer 206 may be used, inpart, to protect and/or preserve the smaller features of the fins 204than can be protected using a conventional organic mask layer. Asdepicted, the first lithographic mask layer 206 may be selectivelydisposed over fin 204 a of the pair of fins 204 a and 204 b, while thefin 204 b is exposed, thereby defining one fin of the pull-down finregion 208, as well as one fin of the pass-gate fin region 214, uponwhich the pull-down transistor and the pass-gate transistor can befabricated respectively, during subsequent fabrication processing.Further, as depicted, one of the first lithographic mask layer(s) 206 isspaced parallel to another first lithographic mask layer 206 which, forinstance, facilitates defining the pull-up fin region 210, upon whichthe pull-up transistor of the SRAM device can be fabricated, duringsubsequent fabrication processing.

FIG. 4 is a plan view of the structure of FIG. 3 with one or more cutmask layer(s) 212 having been disposed over the fin(s) 204, inaccordance with one or more aspects of the present invention. Asillustrated, the cut mask layer(s) 212 are formed orthogonal to thefirst lithographic mask layer(s) 206 disposed over fins 204 at selectedareas, thereby defining pass-gate fin portion 214 a and pass-gate finportion 214 b of the one or more pass-gate fin regions 214, upon whichthe pass-gate transistor could be formed, during the subsequentfabrication processing. By way of example, the cut mask layer(s) 212 mayinclude, or be fabricated of, a photoresist material or a photosensitivedielectric material such as, photosensitive polyimide and may bedeposited using a variety of conventional deposition processes, such as,for example, spin-on coating or the like. In one embodiment, the firstlithographic mask layer 206 and the cut mask layer 212 together defineone example of the first mask layer 216 of the present invention. Asunderstood, in one embodiment, the materials of the first lithographicmask layer 206 and the cut mask layer 212 may be same photoresistmaterials, or different photoresist materials, depending upon theprocessing node in which the SRAM device is being fabricated. Note that,as illustrated, the first lithographic mask layer 206 and the cut masklayer 212 together facilitate defining one fin of the pull-down finregion 208 and pass-gate fin region 214. Although not depicted in thefigures, one skilled in the art will understand, one or moreconventional processing steps may be performed employing the firstlithographic mask layer 206 and the cut mask layer 212 to form a hardmask pattern (not shown) on the substrate 202.

FIG. 5 is a plan view of the structure of FIG. 4 after providing asecond mask layer, such as, for instance, a second lithographic masklayer 218, orthogonal to the cut mask(s) 212, in accordance with one ormore aspects of the present invention. By way of an example, the secondlithographic mask, may be, or include, a photoresist or a photosensitivedielectric material such as, photosensitive polyimide, and may bedeposited using a variety of conventional deposition techniques, suchas, for instance, spin-on coating, or the like. As depicted, the secondlithographic mask layer 218 is disposed over the fins 204, and spacedparallel to the first lithographic mask layer 206, thereby defining asecond fin of pull-down fin region 208 and pass-gate fin region 212.Note that, as illustrated, the cut mask layer 212 is disposed over theadjacent pass-gate fin portion 214 a of the pass-gate fin region 214.Although not depicted in the figures, in one embodiment, the pass-gatefin that may be patterned by the cut mask(s) 212, during the forming ofthe hard mask pattern (not shown), can be recovered using the secondlithographic mask layer 218.

Continuing with FIG. 5, the etching process may be performed selectivelyusing the cut mask layer 212, by employing one or more conventionalanisotropic dry etching processes, such as, for instance, reactive ionetching (RIE), or one or more conventional isotropic wet etchingprocesses to selectively remove a portion of the fin 204, for instance,to obtain one or more patterned fin(s) 204′ (see FIG. 6), particularly,at the pass-gate fin portion 214 a of the pass-gate fin region(s) 214.Further, the etching processes may be accomplished by modifying theprocess parameters so as to remove a portion of the fin uniformly at thecut mask layer 212, leaving pass-gate fin portions 214 a with squareedges, as depicted in FIG. 6. The squared edges of the pass-gate finportions 214 a facilitate encapsulating and/or tucking completely thepass-gate fin portions 214 a within an overlying gate structure, which,in turn, protects the pass-gate fin portions 214 a from subsequentepitaxial growth processes during later epitaxial processing, asdescribed further below. Still further, as depicted, the etchingprocesses may be accomplished using process parameters that areselective to the cut mask layer, without affecting the adjacentlithographic mask layer 218, thereby protecting the underlying adjacentpass-gate fin portion 214 b of the pass-gate fin region(s) 214. This, inturn, facilitates electrically coupling the pass-gate fin portions 214 bof the pass-gate fin region(s) 214, while electrically isolating thepass-gate fin portions 214 a of the pass-gate fin region(s) 214. Suchselective electrical isolation of the pass-gate fin portions 214 aand/or electrical coupling of the pass-gate fin portion(s) 214 b of thepass-gate fin regions 214, advantageously, improves the beta ratio ofthe resultant SRAM device. As used herein, the “beta ratio” refers tothe ratio of the drive currents of the pull-down transistors to thedrive currents of the respective pass-gate transistors. Although notdepicted in the figures, as one skilled in the art will understand, theremaining first and second mask layers, e.g., first lithographic masklayer 206, cut mask layer 212 and the second lithographic mask layer 214can be subsequently be removed utilizing a resist stripping process,such as, for example, ashing.

FIG. 7 is a plan view of the structure of FIG. 6 after providing one ormore gate structure(s) 220 extending at least partially over thepatterned fin(s) 204′, in accordance with one or more aspects of thepresent invention. As depicted, the gate structure(s) 220 may extendover fins 204′, and may overlap fins 204′ in selected areas to operateas, for instance, the pull-down transistor 208, pull-up transistor 210and pass-gate transistor 214 of a SRAM device, respectively. Asdepicted, and described above, each pass-gate fin portion 214 a of thepass-gate transistor 214 is electrically isolated from the pass-gate finportion 214 a of the adjacent pass-gate transistor 214, while thepass-gate fin portion 214 b of the pass-gate transistor 214 iselectrically connected to the pass-gate transistor 214. Further, each ofthe pass-gate transistor is electrically connected to the pull-downtransistor 208. Such selective electrical isolation of the pass-gate finportions 214 a and/or electrical coupling of the pass-gate finportion(s) 214 b of the pass-gate fin regions 214, advantageously,improves the beta ratio of the resultant SRAM device. In one example,the enhanced beta ratio of the SRAM device may be about 2.0 or more.Further, as illustrated, each of the pull-down transistor 208 iselectrically connected to pull-up transistor 210. Additionally, and asone skilled in the art will understand, structure 200 may be expanded toform one or more regions, i.e., regions A and B, to form a SRAM device,as depicted in FIG. 8.

By way of an example, and as one skilled in the art will understand, agate material (not shown) may be provided over one or more layers (notshown), such as, for instance, a gate dielectric layer and/or workfunction layer to form gate structure 220. In one example, the gatematerial may include, or be fabricated of, a metal, and may be formed asa part of a gate-first fabrication process. In this example, the gatedielectric layer may include, or be fabricated of, a high-k dielectricmaterial with a dielectric constant k greater than the dielectricconstant of silicon dioxide (k=3.9 for SiO₂), and may be deposited byperforming a suitable deposition process, such as atomic layerdeposition (ALD), chemical vapor deposition (CVD) or the like. In aparticular example, dielectric layer (not shown) may have a dielectricconstant greater than 4.0, and more preferably, greater than 8.0.Examples of high-k dielectric materials which may be used in thedielectric layer include, but are not limited to, HfO₂, ZrO₂, La₂O₃,Al₂O₃, TiO₂, SrTiO₃, LaAlO₃, Y₂O₃, HfO_(x)N_(y), ZrO_(x)N_(y),La₂O_(x)N_(y), Al₂O_(x)N_(y), TiO_(x)N_(y), SrTiO_(x)N_(y),LaAlO_(x)N_(y), Y₂O_(x)N_(y), and a silicate thereof, and an alloythereof, where x=0.5 to 3, and y=0 to 2. The gate material (not shown)disposed over the gate dielectric layer may include, or be fabricated ofa material such as, for instance, zirconium, tungsten, tantalum,hafnium, titanium, aluminum, or the like. Alternatively, in anotherexample, the gate material may include, or be fabricated of, asacrificial gate material, such as an amorphous silicon (a-Si) orpolycrystalline silicon (polysilicon), which may subsequently bereplaced with a replacement gate material, as part of a gate-lastfabrication process.

In an enhanced embodiment of the present invention, although notdepicted in the figures, the positioning of the cut mask layer 212 (seeFIG. 4) may be selectively altered to modulate the stability of the SRAMdevice. By way of an example, the cut mask layer 212 may be positionedsuch that the resultant patterning processing, subsequent to theproviding of the second mask layer 218 (see FIG. 5), results in removinga portion of fin 204, for instance, to obtain one or more patternedfin(s), particularly, at the pull-down fin region 208, selective to thepass-gate fin region 214, as depicted in FIG. 9. Further, the etchingprocesses may be modified so as to remove a portion of the fin uniformlyat the cut mask layer, leaving the desired pull-down fin portion(s) atthe pull-down fin region 208 with square edges, as depicted in FIG. 9.The square edges of the pull-down fin region 208, advantageously, may betucked completely within an overlying gate structure. Such patterning ofthe pull-down fin region 208 results in the beta ratio of about 0.5.Still further, as one skilled in the art will understand, the processingtechniques described herein may be extended to achieve the desired alpharatio and/or gamma ratio of the resultant SRAM device, therebymodulating the overall stability of the SRAM device. As understood, the“alpha ratio” refers to the ratio of the drive currents of the pull-uptransistors to the drive currents of the respective pull-downtransistors, while the “gamma ratio” refers to the ratio of the drivecurrents of the pass-gate transistors to the drive currents of therespective pull-up transistors.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprise” (andany form of comprise, such as “comprises” and “comprising”), “have” (andany form of have, such as “has” and “having”), “include” (and any formof include, such as “includes” and “including’), and “contain” (and anyform of contain, such as “contains” and “containing”) are open-endedlinking verbs. As a result, a method or device that “comprises”, “has”,“includes” or “contains” one or more steps or elements possesses thoseone or more steps or elements, but is not limited to possessing onlythose one or more steps or elements. Likewise, a step of method or anelement of a device that “comprises”, “has”, “includes” or “contains”one or more features possesses those one or more features, but is notlimited to possessing only those one or more features. Furthermore, adevice or structure that is configured in a certain way is configured inat least that way, but may also be configured in ways that are notlisted.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below, if any, areintended to include any structure, material, or act for performing thefunction in combination with other claimed elements as specificallyclaimed. The description of the present invention has been presented forpurposes of illustration and description, but is not intended to beexhaustive or limited to the invention in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The embodiment was chosen and described in order to best explain theprinciples of one or more aspects of the invention and the practicalapplication, and to enable others of ordinary skill in the art tounderstand one or more aspects of the present invention for variousembodiments with various modifications as are suited to the particularuse contemplated.

What is claimed is:
 1. A method for forming a semiconductor memorydevice, the method comprising: providing at least two mask layers over apair of fin structures extended above a substrate, a first mask layer ofthe at least two mask layers being orthogonal to a second mask layer ofthe at least two mask layers, wherein the first mask layer of the atleast two mask layers facilitates modulating stability of thesemiconductor memory device, without affecting the second mask layer ofthe at least two mask layers; and patterning the pair of fin structures,wherein the first mask layer facilitates partially removing a pair ofpull-down fin regions of the first fin structure of the pair of finstructures, the second mask layer protects a second fin structure of thepair of fin structures to define a fin portion of a transistor, and thefirst mask layer comprises a first lithographic mask layer and a cutmask layer, the first lithographic mask layer being orthogonal to thecut mask layer, wherein the cut mask layer facilitates removal of thepull-down fin regions.
 2. The method of claim 1, further comprisingaltering positioning of the first mask layer of the at least two masklayers to modulate the stability of the semiconductor memory device. 3.The method of claim 2, wherein altering the positioning of the firstmask layer facilitates modifying at least one of a beta ratio, an alpharatio and a gamma ratio of the semiconductor memory device.
 4. Themethod of claim 1, further comprising forming a pair of gate structuresover remaining portions of the pull-down fin regions of the first finstructure, such that each remaining portion of the pull-down regions ofthe first fin structure is tucked under one of the pair of gatestructures.
 5. A method for forming a semiconductor memory device, themethod comprising: providing a first fin structure and a second finstructure extended above a substrate; forming a first lithographic masklayer on the first fin structure without covering the second finstructure; forming a cut mask layer over the first and second finstructures orthogonally to the first lithographic mask layer, whereinthe cut mask layer covers opposing pull-down fin regions of the firstand second fin structures; forming a second mask layer on the second finstructure, the first lithographic mask layer, and a portion of the cutmask layer without covering the first fin structure; and removing aportion of the opposing pull-down fin regions of the first fin structurevia the cut mask layer, wherein the second mask layer prevents theopposing pull-down fin regions of the second fin structure from beingremoved, such that the first lithographic mask layer modulates stabilityof the semiconductor memory device without affecting the secondlithographic mask layer.
 6. The method of claim 5, further comprisingaltering a position of the first and second lithographic mask layersbefore removing the opposing pull-down fin regions of the first finstructure via the cut mask layer.
 7. The method of claim 6, wherein thealtering the position of the first and second lithographic mask layermodifies at least one of a beta ratio, an alpha ratio and a gamma ratioof the semiconductor memory device.
 8. The method of claim 5, furthercomprising forming a pair of gate structures over the first finstructure, wherein each of the pair of gate structures is positionedover a remaining portion of one of the opposing pull-down fin regions.9. The method of claim 8, wherein each remaining portion of the opposingpull-down fin regions is tucked under one of the pair of gatestructures.